1. Field of the Invention
This invention relates to refrigeration systems of the vapor compression type and particularly to devices on the high pressure side of the compressor for intercepting and separating most of the lubricant flowing from the compressor to the condenser and returning the lubricant directly to the compressor oil sump. This invention especially relates to float-actuated oil separators of the repairable type.
2. Review of the Prior Art
There are many devices which operate on the discharge side of the evaporator and the suction or low-pressure side of the compressor, such as a suction accumulator. Such devices are useful for intercepting the liquid and vapor flowing to the compressor in highly variable proportions, for collecting a liquid refrigerant/oil mixture, and for entraining the mixture as droplets with the vapor that is flowing to the compressor. These devices essentially protect the compressor from being damaged by slugs of liquid.
Other devices operate on the high-pressure side of the compressor. Some are disposed between the compressor and the condenser for the purpose of returning oil to the compressor oil sump. Others are located in the line between the condenser and the evaporator and operate entirely on liquid formed in the condenser. They generally function as driers to remove moisture and as filters to remove very fine particles.
An oil return system for a refrigeration apparatus is described in U.S. Pat. No. 3,777,509, for example, in which an oil separator is disposed between a pair of compressors and the condenser. The oil separator returns the oil to the compressors through an oil still.
Such a system is desirable in any refrigeration system of the vapor compression type because the quantity of oil that is needed is thereby minimized, volume available for the working fluid is maximized, and the oil is concentrated where it is needed. Home freezers basically use Refrigerant 12 which is very miscible with oil at all temperatures and dilutes oil easily, so that the oil never coats the interior of the evaporator at the operating temperature of about -10.degree. F. Consequently, home freezers do not need an oil separator.
In large refrigeration systems such as those employed by supermarkets for cooling produce and maintaining frozen items at adequately low temperatures, however, it is particularly undesirable to permit the crankcase oil to circulate throughout the entire system. This is so because such a system uses Refrigerant 502 in which oil is soluble at ambient and higher temperatures but is relatively insoluble at temperatures within the range of -35.degree. to -40.degree. F. In consequence, the oil readily coats the evaporator surfaces so that heat transfer is reduced and thermodynamic properties of the refrigerant itself and of the evaporator are changed.
It is also a pertinent characteristic of such supermarket refrigeration systems at the present time that they have to be defrosted at regular intervals. It is consequently sufficient improvement to existing commercial systems if the accumulation of oil being trapped in the evaporator between defrosting operations can be delayed so that heat transfer properties of the evaporator are not unduly impaired between defrostings.
In large refrigeration systems, such as those used in supermarkets, oil separators are commonly installed in the discharge line of the compressor for separating, containing, and returning refrigeration oil to the compressor crankcase. They may be either disposable or repairable. However, the repairable types are subject to leakage because of frequent cycling of temperatures. Such cycling is caused by rapid heating, when the hot compressed refrigerant passes through the oil separator, and subsequent cooling during the intervals when the compressor is shut down.
Such prior art oil separators comprise a pair of strainers which are disposed in series so that one catches oil on the inside and the other catches oil on the outside. The mesh of these strainers can be varied, but in the prior art it is common to use 40.times.40-mesh brass strainers having crimped bottoms which are fused together by spot welding. The strainers are separated by an "L" shaped baffle and allow separated oil to drip into the lower portion of the cylindrical vessel. In this lower portion, close to the bottom of the vessel, a float assembly is positioned. This float assembly comprises a float ball attached to a lever arm for slideably operating a needle valve within a valve body to open and close a valve seat and allow oil to be sent upwardly through a pickup tube and returned through the top of the vessel to the compressor oil sump.
The strainers are capable of operating with up to 100 times as much dirt as would clog a liquid-line filter-drier. However, they are mainly adapted for catching larger dirt particles than the filter-driers. A magnet is also commonly disposed at the bottom of the cylindrical vessel for catching and holding metallic contaminants.
The float ball must be pressure tight and generally contains a dye penetrant for use in detecting leaks by visual inspection. This dye is placed on the inside of the float ball when it is manufactured and stays there forever if there is no leak. The float ball is strong enough so that it withstands crushing forces up to at least 1,000 psi. The safe working pressure of the oil separator is generally about 450 to 500 psig.
R502 refrigerant sometimes contains as much as 2% oil which is soluble in the refrigerant at compressor discharge temperatures but which is insoluble at cold evaporator temperatures. An oil separator of the prior art will trap 95-98% of all the oil which would normally be circulating throughout the system.
Leakage occurs in repairable oil separators, having a flange top for maintenance of the float assembly, because the top is alternately heated, when the hot compressed gasses flow through the strainers, and cooled, when the compressor is idle. Thus, the gasket expands and contracts and eventually acquires a set so that leakage occurs.
There is consequently a need to make a sealed joint which is not subject to expansion and contraction. It is also desirable to be able to hermetically seal the top of the vessel and at the same time be able to remove the float assembly for inspection, maintenance, and/or replacement.